Spectroscopic Identification of Transition-Metal M[η²-(O,O)C] Species for Highly-Efficient CO₂ Activation

The CO₂ activation by transition metals is important in CO₂ utilization but has proven to be challenging for experimental targets. Here we report first synthesis and spectroscopic characterization of transition-metal M[η²-(O,O)C] species with bidentate double oxygen metal-CO₂ coordination in the [ZrO(CO₂)]⁺ complexes. The Zr[η²-(O,O)C] species yields a CO₂^- radical ligand, showing a high efficiency in CO₂ activation. We find that two important prerequisites are demanded for certain metals to form this intriguing M[η²-(O,O)C] species. One is that the metal center has high reduction capability, and the other is that the oxidation state of the metal center is lower than its highest one by 1. This study highlights the pivotal roles played by the M[η²-(O,O)C] species in CO₂ activation and also open new avenues toward the development of related single-atom catalysts with isolated transition-metal atoms dispersed on supports.